Decreasing TEmperatures
A commonly-held belief is that when it’s cold outside we need a high temperature system to provide a comfortable temperature in our homes and offices.
COWI are actively challenging this belief with practical examples, resulting in
huge savings without loss of comfort.
Over the years many people from all
over the world have visited Denmark
and become acquainted with the
so-called ’Danish Model’ for district
heating. One of the questions frequently
asked by visitors to Danish district
heating schemes is regarding the low
temperatures of operation. Many wonder
how, in a Scandinavian climate, can
Danish district heating operate with such
low temperatures? One explanation is
that Denmark is very flat, allowing us to
operate plants at very low pressures. To
a great extent we also have the possibility
of avoiding heat exchangers between the
network and housing installations.
Even if systems need a high static
pressure and the use of heat exchangers
in substations, it is normally possible to
reduce flow temperatures considerably.
A high temperature may be necessary
during the coldest days, but during the
rest of the year much lower temperatures
will normally be sufficient.
A low operation temperature has the
advantage that the heat loss from the
network is also low. While the supply
temperature can be controlled from
the plant, it is mainly the consumers’
installations that determine the return
temperatures. Therefore, we are now
focussing on creating an overview of and
improving the consumer installations that
fail to reduce the return temperature to the
district heating network to an acceptable
At COWI, together with our customers,
we have set ourselves the goal to find
the lowest possible level for both the
supply and the return temperature. In
the following pages, you can read about
two important projects that point towards
the limit for how low temperature can be
Torben Hermansen
E-mail [email protected]
December 2013
Low Temperatures in Albertslund
Albertslund in Denmark already has
an extensive district heating network.
However, an extensive refurbishment in
the area has led to the opportunity to
significantly reduce the flow temperature,
and realise large savings on heat loss. The
first phase consists of 550 townhouses,
where the district heating is being replaced
to operate at a flow temperature of just 50
”The terraced houses are within an
existing supply area consisting of mixed
residential and community buildings.
The challenge is therefore to make the
new low-temperature system interact
with the existing system. To begin with, a
temporary shunt will be established in a
specially designed cabinet. Once the entire
project is complete, the temporary shunt
will be replaced with permanent plant.”
says COWI’s Senior Project Manager,
Theodor Møller Moos.
in the heat exchanger and pipes at any
one time to a level where it cools quickly
when not in use and Legionella growth is
The work carried out in Albertslund
provides important new knowledge to
the research project ”Establishment of
low-temperature district heating in existing
district heating supply”. As part of this
project, data is collected on projects
where low temperature district heating is
installed to assess performance and to
help future development. Particularly how
low temperature areas can be successfully
operated as part of a wider high temperature network.
The renovation of the dwellings includes
the addition of new energy efficiency measures, which together will reduce the heat
demand to 60 per cent of the demand
before renovation. With the establishment
of low-temperature district heating, the
heat loss is expected to be halved compared to conventional district heating. The
dwellings have underfloor heating, which
can run at low supply temperatures, and
hot water is provided via a heat exchanger
in each dwelling. The design of the interior
pipework limits the amount of water held
Renovations are now complete in a quarter
of the homes in Albertslund. The residents
have moved in, and are using the new
low-temperature district heating. The entire
renovation project is scheduled to be
completed in 2015.
Theodor Møller Moos
E-mail [email protected]
District Heating to Gentofte’s Villas
Gentofte is a suburb of Copenhagen
formed from a number of small towns
which were amalgamated together as the
city spread. Therefore, many of the single
family houses are original and built in the
late 1800s or early 1900s. Until now, the
majority of the many beautiful properties
in Gentofte, including several embassies,
have been heated with individual natural
gas boilers. But natural gas will soon be
a thing of the past in Gentofte, as district
heating pipes are steadily spreading
In Phases 1 and 2 alone, there are more
than 55 km of new main and distribution
”We are focusing on using the lessons
learned from the first phases of the project
to optimize the planning of subsequent
stages. For example, it is important
that connections are made quickly and
constantly throughout the project to
ensure regular earnings to Gentofte District
Heating. Therefore, we will begin with the
small pipes and install the larger pipes in
sections. Careful planning of the sections
will both minimise disruption and will
COWI is Consultant to Gentofte District
ensure that payback on the investment
Heating on the extensive expansion
of the large pipes can begin as quickly as
project, which started in 2011 and will
possible.” says COWI’s project manager,
be phased out over six stages through to 2026. Peter Bode Nielsen.
District Heating Crosses
Major Motorway
The area of Vinding, near Vejle in Denmark
has, to date, been heated using natural
gas. Although close to the extensive
district heating system in Vejle, Vinding
is located on the other side of a four lane
motorway, which is a major transport route
through Jutland.
COWI have assisted Mølholm District
Heating to overcome the physical barrier
of the motorway, to bring district heating
to Vinding. This will help to reduce carbon
emissions and give a more sustainable
source of heat to the area.
The transmission line is laid under the
motorway by means of directional drilling
15m below the asphalt, in accordance with
the Danish Road Directorate rules.
COWI has participated throughout the
entire process and has delivered: socioeconomic analyses, project proposal,
tender material, marketing, contract
negotiations, client consultancy and
Mogens Thomsen
E-mail [email protected]
Once the final phase is complete, approximately 14,000 dwellings in Gentofte
will have the opportunity to connect to
district heating. Although connection is
not expected to be 100 per cent in 2026,
the new connections will certainly result
in a significant reduction in municipal CO2
emissions. Gentofte District Heating plans
to continue to roll out further environmentally sustainable solutions to further reduce
overall CO2 emissions. COWI are currently
working with Gentofte District Heating to
develop further ideas for the future, such
as the possibility for reducing temperatures
across the network.
Peter Bode Nielsen
E-mail [email protected]
Laser Scanning has Many Advantages
COWI is using 3D-laser scanning as an
important tool to assist with the extension
of a large heat exchanger station in
Rødovre, a suburb of Copenhagen.
”Because of on-going renovations and
additions to the plant over the years, the
original drawings do not include all pipes
and components. Therefore we have
scanned the station to create a complete
overview of the installation. The scanned
model will subsequently be transformed
into a 3D model, which we can use to
visualise changes to the stations.” says
Project Manager, Casper Lind Larsen.
“The scan and the subsequent processing
into a 3D model gives a really good basis
for the design phase, since it means that
the designs are based on a definitive
model, which is known to be accurate
and up to date.
Instead of going out repeatedly with a
measuring tape, we have a virtual model
where we can measure all distances and
in which we can move around, as if we
were on site. When we have finished creating a new design, we can put it back into
the original scan, to give a good picture of
how the changes will look.”
At the same time the tool provides a better overview of the installation and makes
it easier to follow the design process. The
3D model is used on an ongoing basis
at the status meetings to keep the team
updated. And finally, the client can have
a projected view in the original 3D model
(see the illustration).
Casper Lind Larsen
E-mail [email protected]
Aerial Survey
Huge savings
In the Dutch town of Purmerend,
the district heating supply company,
Stadsverwarming Purmerend B.V., has
reduced the daily water loss from the 281
km long pipeline network by an incredible
70 per cent. This has been possible
thanks to a small COWI aeroplane with a
heat-sensitive camera attached.
By surveying the area with a thermographic camera, COWI have located
155 potential ’hot spots’. Each hot spot
was examined in more detail, and at the
locations where leaks were found, the
pipes have been refurbished or renewed.
One of the largest underground leaks
found in Purmerend covered an entire
intersection. The leak originated from a
faulty weld, which was made when the
district heating pipe was installed twelve
years ago. It is possible that the weld
has been leaking for up to twelve years
undiscovered, wasting a huge amount of
water and heat, until it was discovered by
the thermographic survey (see illustration).
Not only do leaks cause losses of water
and heat, but also loss of pressure in the
transmission system. In some systems
this can make it difficult to provide a
consistent heat supply to consumers
located furthest from the pumps.
Potential issues can be identified using a
thermographic survey, and a subsequent
renovation programme of the leaks. In this
way, thermography from the air is leading
to energy savings as well as increased
security of supply.
Emrah Øztunc
E-mail [email protected]
Optimization which Pays Off
TVIS (Trekantsområdets Varmetransmissionsselskab) is the company
responsible for the distribution of heat
through an intercity transmission network
connecting several cities in Denmark.
TVIS owns, operates and maintains the
transmission network and the related
exchanger stations which transport
heat from major power and industrial
process plants in the area (including
natural gas, waste to energy and an oil
refinery) to district heating networks in four
municipalities. Transporting the heat as
efficiently as possible is therefore a primary
goal for TVIS.
To ensure optimum efficiency, TVIS
use dynamic modelling and control via
TERMIS Operation. TERMIS was used to
establish a dynamic model for the entire
transmission network, which was coupled
to a new SCADA system. Together they
give a detailed insight into the operation of
the transmission network, allowing TVIS
to achieve more accurate control and
monitoring and realise significant efficiency
By supplementing the optimisation tool
with the program PRESS Production
Temperatures 2010-2011
Optimization, TVIS has also enhanced
its ability to buy heat from the cheapest
supplier at the correct temperature.
PRESS Production Optimization connects
data such as the weather forecasts and
demand monitoring, with heat prices
at TVIS’ different suppliers. TVIS use
this information to buy heat a month in
advance from the cheapest supplier at the
predicted temperature required. The risk is
that if the temperature turns out to be too
low compared to the demand it must be
supplemented from other more expensive
sources. Therefore, the predictions made
using the information from PRESS must be
consistently accurate.
PRESS Production Optimization is
standard software, which has been
adapted to TVIS. TERMIS Operation
and PRESS is a large investment but, as
expected, it has proved to have a good
rate of return. In fact, the system has paid
for itself after just one year!
Thomas Østergaard
E-mail [email protected]
Temperatures 2011-2012
Graphical representation of the operation before (2010-11) and after the commissioning of the new forecasting system (2011-12).
Geothermal Energy for
District Heating
In Sønderborg, Denmark, a new geothermal plant uses naturally occurring hot
water from under the ground as a heat
source for district heating. Together with
biomass the geothermal source almost
totally replaces the natural gas at the
Sønderborg plant, with heat from natural
gas now representing only five per cent
of Sønderborg Fjernvarme’s total energy
consumption. The change to renewable
geothermal heat has also contributed to
the reduction of the overall CO2 emissions
from the plant by 90 per cent.
The geothermal plant is located across two
sites, with the bore holes located about
5km from the main Sønderborg heating
plant. At the extraction site, geothermal
water at approximately 48 °C is pumped
up from one bore hole and passed through
a heat exchanger before being reinjected
to another bore hole at approx. 15 °C.
The geothermal plant in Sønderborg is the
third of its kind in Denmark. But, unlike
the others, Sønderborg is integrated with
a biomass-fired boiler plant. The biomass
boilers produce hot water at 175 °C
to provide the energy to run four large
absorption heat pumps. The heat pumps
increase the temperature of the geothermal water to 80 °C for use in the district
heating network.
and a solution was found whereby water
at 48 °C could be used from a borehole
of 1,200 m. COWI were responsible for
the design, procurement, contracting
and construction of the plant. COWI are
now starting to investigate 27 sites for the
Danish Energy Agency in order to assess
the possibilities for utilising geothermal
water from other sites. This could pave the
way for the development of many geothermal plants like Sønderborg in the future.
›› Four absorption heat pumps raise the
water temperature to approx. 80 °C
and simultaneously provide water at
12 °C for cooling of the geothermal
›› The geothermal water has a temperature of approx. 48 °C when extracted.
When the water is returned to the
ground, the temperature is about
15 °C.
›› The 175 °C hot water that drives the
heat pumps is produced by a new
wood chip-fired boiler plant.
›› The geothermal energy contributes
with approx. 12 MW of heat. An
additional 30 MW is provided by the
biomass boiler plant, which is also
equipped with a system for cooling of
the flue gas.
A Good Investment
Originally the boreholes were expected
to provide water at 68 °C at a depth of
2,000 m. However, this was not possible
Parallelvej 2
2800 Kongens Lyngby
8000 Aarhus C
E-mail [email protected]
COWI Aarhus
Jens Chr. Skous Vej 9
Niels Otto Clausen
+45 56 40 00 00